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<a name="Naming-conventions-1"></a>
<h4 class="subsection">6.4.1 Naming conventions</h4>

<p>According the Fortran standard, valid Fortran names consist of a letter
between <code>A</code> to <code>Z</code>, <code>a</code> to <code>z</code>, digits <code>0</code>,
<code>1</code> to <code>9</code> and underscores (<code>_</code>) with the restriction
that names may only start with a letter.  As vendor extension, the
dollar sign (<code>$</code>) is additionally permitted with the option
<samp>-fdollar-ok</samp>, but not as first character and only if the
target system supports it.
</p>
<p>By default, the procedure name is the lower-cased Fortran name with an
appended underscore (<code>_</code>); using <samp>-fno-underscoring</samp> no
underscore is appended while <code>-fsecond-underscore</code> appends two
underscores.  Depending on the target system and the calling convention,
the procedure might be additionally dressed; for instance, on 32bit
Windows with <code>stdcall</code>, an at-sign <code>@</code> followed by an integer
number is appended.  For the changing the calling convention, see
see <a href="GNU-Fortran-Compiler-Directives.html#GNU-Fortran-Compiler-Directives">GNU Fortran Compiler Directives</a>.
</p>
<p>For common blocks, the same convention is used, i.e. by default an
underscore is appended to the lower-cased Fortran name.  Blank commons
have the name <code>__BLNK__</code>.
</p>
<p>For procedures and variables declared in the specification space of a
module, the name is formed by <code>__</code>, followed by the lower-cased
module name, <code>_MOD_</code>, and the lower-cased Fortran name.  Note that
no underscore is appended.
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